Does the regular 12V car battery in EVs last a very long time? I imagine it’s not going through charge/discharge cycles, basically at full charge all the time?
And, if I turn an EV off (whatever that means) but turn the radio on, am I draining the 12V battery? Let’s say I was tailgating, or even better, at a drive-in (so that I had to keep the running lights off) and listening through the FM simulcast. Am I ask risk of not being able to start the car, whatever that means for an EV? Or, does the EV just always keep the 12V battery at full charge, unless something goes wrong with the electronics?
My experience is that they do not last a long time.
Yes the 12v runs the infotainment systems, the locks, and systems that engage the traction battery. Dead 12v and the EV won’t start. Happen to my wife in her 2019 Leaf after she left it parked in a spot with blinkers flashing for … a while.
Not sure if the radio can be kept on with the car off, but various systems that run in the background can still draw on it and drain it. Some vehicles have schedules or algorithms to trickle charge the 12v from the traction battery when the car is parked and turned off.
Yeah, I think this is one of those things where there’s variation between different EV manufacturers & models. I don’t believe there is a single unified, standard approach to this (how they handle 12V battery recharging from the big traction battery). Check your user manual or car-specific forums for details.
Some have a “Utility mode” (Kia/Hyundai) or “Camp mode” (Rivian) or Muskdaddy’s various modes (Tesla) or similar that will keep the traction battery engaged and use that to power the AC, radio, etc. directly (using a DC step-down converter, I think). On mine, you have to keep the car in READY mode and not the accessory mode (or you’ll drain the 12V). On some there might not be a designated mode for this and you’ll have to try to manually bypass the auto-off timer somehow.
I mean, the answer is actually close to vehicle (and sub-model) specific. Using my wife’s 2024 Rav4 Prime (PHEV) as an example, it has a half dozen modes that it can use, including “room” mode, where if it’s plugged in to a power source (like at an RV or other full featured camping area) you can run internal lights, infotainment, and climate control!
Her tricked out XLE also has a dedicated 120v plug in the back, which explicitly pulls from the traction battery for tailgate parties, camping and the like, rated to 1500w IIRC, and can be set to turn on the ICE engine for recharging if the traction battery gets low.
The most common complaint I head about BEV/PHEV 12v batteries is that the margin for lifespans is a lot lower than some ICE vehicles, especially with the tiny 12v batteries that are common (and often “hidden” out of sight out of mind). So, while you might expect to get 4-6 years out of a legacy ICE vehicle, you should replace promptly at 3 years with a BEV/PHEV.
[ ETA: simulpost with Reply covering some of the same things!]
This seems like such a no-brainer for the car makers, so I’m really surprised at the answers. They have this giant traction battery that can be engaged whenever necessary to keep the 12V charged up, but if I leave my parking lights on overnight by accident, I still wake up to a dead car. So dumb.
I know one of the EV makers has a built-in jump start system. Wow, fancy. The idea that I would have to jump my 12V when my car has 200 miles of range on it is blowing my mind.
The giant traction battery is typically disengaged while parked by disconnecting electro-mechanical switches (contactors powered by the 12V). The physical electrical connection is severed for safety reasons.
Why they then let you ignore the safety and keep it on with a special mode… well, I don’t know. Presumably you’re in there and would notice if the car started exploding.
IMHO (so not factual) another reason is part providers for automakers want the widest range of utility - so the infotainment system, lights, etc. are probably all designed to work with the traditional 12v system and can be used in straight ICEs, Mild hybrids, true hybrids, PHEVs and EVs. And producing for that scale means economies of cost which is attractive…
Though with the “success” of the Cybertruck, I don’t know how popular that is among other EV makers…
Speculation as well:
I would think that minor things like head units and other displays (which are just a tiny portion of the overall cost) would be different enough in EVs anyway, since the ergonomics of them are so different (smaller or nonexistent frunks leading to different steering wheel and HUD and dashboard configurations, plus the lack of shifters and sometimes not even having a steering column and using drive-by-wire). I don’t know how much of the in-cabin parts they can really share with their ICE cousins. And certainly the UIs would have to change to cram in all the EV-specific dials. Maybe in the earlier days when manufacturers were still repurposing ICE chassis and bolting on EV motors, but with the newer ones being custom-built EV platforms (often shared between manufacturers now, but usually all for BEVs, I think…?). I dunno. Interesting to think about.
I mean, it’s dumb for any car to let you drain the 12V battery by leaving something turned on. Just automatically turn off whatever it is, if it’s been too long.
Still seems like it should be able to connect the traction battery just long enough to charge the 12V to some minimum safety level (50% or so) instead of letting it drain completely, right?
Maybe some do? From that article:
In most EVs, if you leave them parked for an extended stretch, they will periodically wake up, click on the electrical connectors for the traction battery, and charge the 12-volt battery so that it doesn’t run dry. If the 12-volt battery in an EV fails, you probably won’t be able to unlock and start it, even if the high-voltage battery still has juice.
Maybe it stops if it detects an aging or dying 12V battery so it doesn’t keep wasting the traction battery? It also takes some amount of power to keep monitoring the charge level of the 12V. Combine it with adverse weather etc and maybe sometimes it just sometimes fails to detect the “I should charge the 12V” state? It’s interesting to ponder but I don’t know the actual engineering in use.
Not an EV but a hybrid: just yesterday I replaced the 12V battery in my 8 year old Prius. Several times in the last few months it failed to start after leaving it undriven for 2-3 weeks. A couple of days ago it failed to start after I hadn’t driven it for 6 days. That was enough for me.
I don’t think my Prius has any mode that uses the traction battery to power the car electronics. My wife actually asked my why the traction battery doesn’t prevent start failures if the 12V is low, and I mumbled something about different voltages. But I don’t know the details.
Obviously, if you drain the big battery, it cannot top off the 12V battery. For my Tesla, Ive had to change the 12V once - they seem to last about 3-4 years. (YMMV). I’ve sat in the car with the radio and heat running for almost an hour, no problem, but that may be a side effect of the phone in my pocket being a “key present”. I saw someone towed to a charger in Mississauga with a totally dead car - they fortunately did not close the door, so they could crawl into the trunk and pop the clip for the charger plug - but I left before they got charging going. (I looked it up later - they needed a 9V to pop the frunk, remove the plastic lining and boost the 12V battery until the computer boots). Newer Teslas have a 16V smaller battery so the procedure is somewhat different.
If the 12v battery in Chevy Bolts starts to deteriorate the car will start to do all sorts of weird but not very useful things. Disconnecting the battery for a few minutes will often get things going again so you’re not stuck on the road. Following the advice of posters on the Bolt owners message board I peruse, I carry in the glovebox a 10mm socket plugged into a palm-sized ratchet.
We had the same problem with our 2004 Prius. My wife retired a year ago, and has rarely driven it since, so after being barely used for a couple months, the 12V battery died.
After I replaced it, I bought one of these, a solar battery charger. It mounts with suction cups in the back passenger’s side window, and connects directly to the battery, constantly maintaining its charge.
I only installed it a few weeks ago, so no long-term experience yet, but so far, so good.
I have a plug-in trickle charger but since I don’t park the car in my garage, it’s not very convenient to keep it connected to the car. I keep a portable charger in the car that I can use to jump start it in an emergency. I’ve only had to do that twice, and the car was at home both times, not stranded out on the road.